1. Field of the Invention
The present invention relates to a metal gasket. More particularly, the present invention relates to a metal gasket for a semiconductor fabrication chamber that is capable of preventing metal contamination in the chamber.
2. Description of the Related Art
With the trend in semiconductor devices toward high function and high density, it is very important to reduce contamination in semiconductor fabricating apparatuses and processes. A semiconductor fabricating process is performed using various apparatuses, such as a diffusion furnace for growing a layer or diffusing impurities at a high temperature, a plasma apparatus for chemical vapor deposition (CVD) or etching under a high vacuum, and an apparatus for implanting ions or depositing metals.
A plasma apparatus activates a gas using a high frequency power and creates plasma with high-energy ions or radicals to form or etch a thin film. Therefore, because plasma causes arcing of a plasma reactor, sputtering, and stripping of reactive byproducts, the plasma apparatus acts as a main source of contamination in a semiconductor fabricating process.
During the semiconductor fabricating process, particles may be created and metal ions may be contaminated. The particles and the metal ion contamination may result in a defective pattern, poor pressure resistance of an insulating layer, generation of a junction leakage current, and shortening of a semiconductor device lifetime. That is, semiconductor devices may be critically damaged by such contamination.
Accordingly, sources of contamination and methods for the removal thereof have been actively studied. To remove contamination sources in a semiconductor fabricating process using plasma, various approaches, such as varying the material and structure of a semiconductor fabricating apparatus and changing or adding a process, have been studied and applied recently.
The following tables, TABLE 1 and TABLE 2, present PN and RTN (rapid thermal nitridation), HDP (high density plasma), and SiN (silicon nitride) process conditions and resulting levels of metal contamination.
TABLE 2 shows that the contamination level of copper (Cu) is very high in the PN and RTN process. A search for the source of the Cu contamination indicates that an Au anti-corrosive coating layer of an Au-coated Cu gasket for an airtight vacuum is attacked, exposing a Cu layer of a base plate. Since the Au coated Cu gasket is installed below a chamber, the exposure of the Cu layer results in contamination of the chamber. Since a Cu gasket is generally highly corrosive, a chamber using NH3 gas employs the Au-coated Cu gasket. Nonetheless, the Au is inevitably attacked and the chamber contaminated with Cu due to a corrosive gas and others. The damage of the Au-coated Cu gasket results from a corrosive gas (e.g., PH3 or NH3) and relatively high process temperatures.
Various analysis techniques are used to analyze elements of reaction products that are produced on a surface of a used Cu gasket, some of which are explained in detail below.
In analysis using an energy dispersive X-ray spectrometer (EDX), Cu, O, and P are detected and the reaction products are determined to be Cuxe2x80x94O oxide and Cuxe2x80x94P compound. In analysis using a scanning electron microscope (SEM) relative to a gasket base plate surface where the reaction products are stripped, Cu and O are detected as main elements. These results show that the reaction products are stripped to expose the Cu layer, which acts as the Cu contamination source of the chamber. In analysis of phases of the reaction products using an X-ray diffractometer (XRD), six kinds of phases are detected, as shown in FIG. 6. As main phases, CuO and Cu2O are detected. The conclusion attained from the XRD analysis result is that each of the phases is gradationally formed.
A mimetic diagram of reaction products produced at a conventional Au-coated Cu gasket is illustrated in FIG. 7.
Referring to FIG. 7, a Cu gasket initially has a layer type of Cu/Au. After being installed at a chamber, the Cu gasket has a layer type of Cu/Au/Auxe2x80x94Cu/Cu2O/CuO, Cu3P because a process temperature rises and a corrosive gas is used. However, since an unused gasket retains a layer type of Cu/Au, a source of Cu is needed for making such reaction phases. Namely, in order to change the Cu/Au into the Cu/Au/Auxe2x80x94Cu/Cu2O/CuO, Cu3P, the Cu must be diffused to the Au.
Therefore, Cu-to-Au diffusion is needed for producing reaction products of the foregoing type. According to xe2x80x9cMetals Handbook, Surface Engineering of Nonferrous Metals,xe2x80x9d ASM International, it is reported that Cu is diffused to Au because a temperature at a Cu/Au interface rises. A diffusion coefficient of Cu is much greater than that of Au. The Cu and Au have the same lattice structure and are subjected to a complete solid solubility within all composition ranges. Thus, the Cu is diffused to the Au due to the increase in temperature. A diffusion speed of Cu is high and an atom size thereof is small. The Cu is attacked by ammonia (NH3), which is very corrosive to Cu, from a surface of Cu oxide and an area where reaction products are stripped. As a result, since the Cu elements are separated and transferred to a chamber, not only the chamber but also a wafer are contaminated.
As described above, when an anti-corrosive layer of an anti-corrosive coated gasket used in a semiconductor fabrication chamber is damaged, base elements are diffused to the chamber, causing metal contamination of the semiconductor fabrication chamber. Accordingly, it is a feature of an embodiment of the present invention to provide a metal gasket that is capable of preventing metal contamination.
In order to provide this and other features, a metal gasket for a semiconductor fabrication chamber is provided, including a base plate, a diffusion barrier layer and an anti-corrosive coating layer, wherein the diffusion barrier layer and the anti-corrosive coating layer are sequentially formed on the base plate to prevent elements of the base plate from being diffused to the anti-corrosive coating layer when a process is performed in the semiconductor fabrication chamber. Preferably, the base plate is made of Cu, and the anti-corrosive layer is made of Au. Further, the diffusion barrier layer is preferably made of one selected from the group consisting of Ti, W, TiN, and Ni.
The diffusion barrier layer may include a first diffusion barrier layer and a second diffusion barrier layer. In a two-layer construction, preferably, the first diffusion barrier layer is made of Cr and the second diffusion barrier layer is made of Ni.
Preferably, a metal gasket according to the present invention may be used in a semiconductor fabrication chamber when a corrosive gas is used as a process gas, and may be installed at a chamber where a metal is deposited at a relatively high temperature, e.g., 700xc2x0 C. or higher.